Editor's Comments. Margaret (Skeels) Stevens produced this
paper while a student at the University of Michigan. She was a
productive scholar and teacher at Lamar University in Beaumont, Texas,
before her recent retirement. This is the seminal paper on the
mastodonts and mammoths of Michigan. It not only details the known
records of these animals in the state, but discusses aspects of their
taphonomy (mode of death, burial, and fossilization) and biology. The
idea that Skeels put forth--that the deep muck and peat and floating
mats of vegetation ("quaking bogs") in the late Pleistocene were natural traps that these heavy animals would have broken
through--is still accepted as primary taphonomic event involved in the
fossilization of these proboscideans. The fact most fossil proboscideans
in Michigan have been excavated from former shallow basins of kettle bog
sites attests to this hypothesis.

Nevertheless, the fact that these animals are almost always found
as scattered parts rather than whole skeletons indicates that other
taphonomic events occurred. Several of these have been addressed by
Daniel C. Fisher of the University of Michigan (e.g., Fisher 1984a,b).
It is quite possible that the animals merely become stuck, rather than
completely buried in bogs. Here they could have died of starvation and
been scavenged by humans (see Barondes' 1996 report on the St.
Johns, Michigan mastodont excavated by Daniel Fisher and Fisher 1987);
or weakened ones could have been killed by human hunters. Then the
animals could have been butchered at the site, the edible portions
carried away, and the remaining parts discarded in the boggy areas in
which they were found. There, fossilization would have occurred.

The lack of smaller vertebrate fossils from proboscidean sites in
Michigan was attributed by Skeels to the possibilities that, because of
their smaller size, their remains might have been overlooked, considered
recent intrusions, or because they look "... very much like pieces
of branches or roots that are sometimes present in muck or peat."
Since Skeels (1962) many sites have been carefully excavated by
professional vertebrate paleontologists, and there is still no question
that small vertebrates are exceedingly rare at these localities. I
suggest that at least one part of the problem is due to the fact that
the highly fibrous plant matrix in which Michigan proboscideans are
found is almost impossible to dissociate, thus standard wet-screening
methods do not work; and that another part of the problem may be do to
the erosion and eventual loss of small vertebrate bones due to the
highly acidic conditions of bogs and bog remnants. Most of the C14 dates
in this paper are too young.

INTRODUCTION

Fossil mammals are known only from the Late Pleistocene of
Michigan. If earlier Cenozoic deposits ever were present in Michigan
they were destroyed by glacial ice that four times overrode the state.
The American mastodon and Jefferson mammoth were the largest Pleistocene
animals to walk on Michigan soil. Most of the information concerning
these large mammals in the state must be sought in newspaper reports of
individual finds. However, O.P. Hay (1923) reported upon all Michigan
Pleistocene mastodon and mammoth remains known to him. Case and others
(1935) reported the occurrences of the Jefferson mammoth from Glacial
Lake Mogodore in Cass County. Later in the same year, Case and Stanley
(1935) reported on the Bloomfield Hills mastodon. Archie MacAlpin (1940)
summarized all known finds of the American mastodon in Michigan but did
not publish on the mammoths. The purpose of this paper is to place on
record all known occurrences of both the American mastodon and Jefferson
mammoth in the state, including those discovered since 1940, and to make
available to the citizens of Michigan an account of these interesting
mammals.

Most of the fossil remains of these animals found in the state have
occurred in swamps and bogs. Such areas owe their origin to the manner
in which the last glacier melted; the majority of the lake depressions
were formed at the time of the retreat of the last ice sheet. As the ice
front retreated large blocks of ice were left behind, buried under the
glacial outwash sediments. For a time such ice blocks were protected
from the warmth of the sun by the gravel, sand, and silt that covered
them. Eventually, however, these ice remnants melted, leaving
depressions in their place. Although most of these were of small size,
others were quite large. Geologists refer to the smaller ones as kettles
or kettle holes. If silt or clay washed into these depressions it sealed
them, and water would then accumulate to form a pond or lake. In most
cases such depressions contained water only in the spring, but if they
went below the water table a permanent pond or lake resulted. Over the
years such ponds and lakes continued to receive sand, silt, and clay
from flood waters, and additional material from vegetation growing
around their edges. In time at least some of these bodies of water,
particularly the shallower ones, became filled to levels where aquatic
and semiaquatic vegetation could encroach upon the open water. Thus a
bog was formed where an open pond or lake had once existed. Wherever
water was shallow, plant material extended down through the water to the
bottom, but where the water deepened the vegetation often formed a mat
that floated over part of the water surface. Partially or completely
filled depressions of this sort exist in Michigan today and are called
"quaking bogs." The process of filling, however, is one that
still continues and depressions in all stages can be found in the state.
Floating mats of the nature described are unsafe; a heavy animal
venturing too far out on one often breaks through. Many times such an
animal is unable to climb back onto the mat, becomes mired, and
eventually drowns. These bogs apparently were places of retreat for
mastodons and some mammoths during the winter months. They would have
been protected from strong winds, and the surrounding forest would have
offered abundant food. But the deep muck and peat and the floating mats
of vegetation, though partly frozen, were potential traps.

Most mastodon remains in southern Michigan are associated with
muck, peat, and marl. Chances for preservation are good in bogs because
there is immediate burial. The body of an animal that dies on high
ground is seldom preserved because predators and scavengers scatter the
bones. Such exposed bone usually becomes decayed or badly weathered
before it can be carried downslope to a lake or stream to be preserved
in the sediments deposited there. Bone that comes from a bog is usually
very dark colored, dark brown or black, due to the acids produced by the
decaying organic matter.

Because of their larger size, mastodons are the most commonly found
mammalian fossils in Pleistocene deposits in Michigan Smaller animals
such as elk, deer, wolves, and beavers are probably much more abundant
in bog deposits, but because of their smaller size their remains may be
overlooked or considered those of recent forms. Moreover, these smaller
bones often look very much like the pieces of branches or roots that are
sometimes present in the muck or peat. Recovery of the smaller
Pleistocene mammals of Michigan would do much to increase our
understanding of these Ice Age forms.

THE AMERICAN MASTODON

The ancestors of the American mastodon reached North America from
Eurasia via the Bering land bridge during Miocene time, approximately 18
million years ago. These early proboscideans (animals with a trunk) were
subtropical forms, not the cold-loving animals that some of their
descendants became. During the Ice Age (Pleistocene) the American
mastodon gradually became adjusted to cooler conditions, so that by the
time of the last of the four glaciations they were well adjusted to life
in cold northern (boreal) forests.

Fossil remains indicate that only two species of the Proboscidea
lived in Michigan during the Late Pleistocene. These were the American
mastodon (Mammut americanum) and the Jefferson mammoth (Mammuthus
jeffersoni). These two forms are usually known, collectively, as
"mastodons" or "elephants" to the uninformed person.
In reality they represent two very different types of animals. The
similarities between them are large size, columnar (graviportal or
pillar-like) limbs, a proboscis (trunk), and large tusks (specialized
incisor teeth). Important differences occur in skull shape and tooth
structure, as explained below. Moreover, they lived in quite different
habitats.

It is rather unfortunate that the two generic names, Mammut and
Mammuthus, are so similar. Both words stem from the barbaric word
mammut, which means "earth-burrower" (Lucas 1935, 157). The
term is believed to have originated during the Middle Ages when the
Eastern European farmers assumed that these beasts were large burrowing
monsters because their bones were commonly found buried in the soil. The
peasants had never seen a living elephant.

Cuvier's term Mastodon has frequently been used as a generic
name for the American mastodon, and "Mastodon americanus" is
still used in a loose sense today because it is so prevalent in the
literature (Jepsen 1960). However, Blumenbach's (1799) name Mammut
is the earlier and accepted generic name.

Following is the classification of the Late Pleistocene mastodon of
Michigan.

The foregoing are synonymous names, names that have been used in
past years for the American mastodon in Michigan.

Characters of Mammut americanum. -- The tusks are without enamel.
The upper tusks are large and round with slightly indicated annular growth rings (Osborn 1936). The lower tusks, when present, are small,
straight, and circular in cross section (Plate. II, Figure. 3), but they
usually were lost by mature individuals. One specimen (UMMP 37811) in
the University of Michigan Museum of Paleontology has the two lower
tusks present one in each of the lower jaws. The maximum length of the
left lower tusk is 241.0 mm; the maximum transverse diameter, at the
base of the tooth, is 47.0 mm. The vertical diameter, at the base of the
tooth, is 40.05 mm. The diameter at the tip, which is blunt and
polished, is 27.0 mm. The depth of the alveolus (socket) is 170.5 mm.
The tusks in mastodons are the upper and lower second incisors; the
first and third incisors in each jaw failed to develop.

Tusks of the mastodon and the mammoth consist of ivory, which is a
complex type of dentine. Dentine is not so hard as enamel and therefore
does not lend itself as well to fossilization. Well-preserved tusks of
mastodons or mammoths have not been found in Michigan. Tusks when found
are usually very friable so that the layers of ivory split and break off
in small pieces.

One of the differences between the American mastodon and the
mammoth is the way the tusks leave the skull. In the mastodon they
project more or less horizontally from the skull, curving at first
outward and later inward (Plate I, Figure 2) in the course of growth,
whereas in the mammoth the tusks leave the skull more nearly vertically,
curve downward and outward, then begin the curve that brings their tips
inward toward each other (Plate I, Figure 1).

[FIGURE 1 OMITTED]

The size of the tusks in both mastodons and mammoths differs
between the sexes. The male individuals of both species possessed
heavier, larger, and longer tusks.

Mastodons apparently used their tusks to pry off and possibly to
break into small pieces the branches upon which they fed, in much the
same way that the living African elephant will rip a limb from a tree,
stand on it with both feet, and break it in half with one of its tusks.
Only one tusk is used in this operation, never both. Elephants and
mastodons were thus "right" or "left handed." When
both of the tusks are recovered with the skull of a mastodon, one of
them is usually shorter than the other and shows breakage and polish at
the tip (Plate I, Figure 2). This has often been overlooked in mounted
specimens; tusks have frequently been restored equal in length.

The cheek teeth of the American mastodon consist of six on each
side of each jaw. The first three teeth of the six are known as milk or
deciduous premolars and the last or hinder three as permanent molars.
The individual teeth, exclusive of the tusks (incisors), are designated
in the upper jaw as D[p.sup.2], D[p.sup.3], D[p.sup.4], [M.sup.1],
[M.sup.2], and [M.sup.3]. The symbol "Dp" stands for deciduous
premolar and "M" for permanent molar. The lower individual
teeth are designated as D[p.sub.2], D[p.sub.3], D[p.sub.4], [M.sub.1],
[M.sub.2], and [M.sub.3]. In a reference to both the upper and lower
last molar, for example, the symbol would be written as [M.sub.3.sup.3].
In the American mastodon D[p.sub.4.sup.4], M 1/1, and [M.sub.2.sup.2]
each consist of three transverse ridge crests, or lophs, which are
formed by two cusps. [M.sub.3.sup.3] has four lophs and a vestigial heel
behind the last ridge crest (Figure 1B; Plate II, Figures 1 and 2). In
some individuals, there are five lophs across the third molar.
Cuvier's term, mastodon, refers to the nature of these cusps. The
word when broken down into its Greek roots means "nipple tooth" (Palmer 1904, 401).

The teeth increase in size from the fourth premolar to the last
molar. The size of each tooth varies somewhat in different individuals,
as well as in the same individual. See Table 1 for measurements of
American mastodon teeth in the University of Michigan Museum of
Paleontology.

There is no juvenile specimen in the University of Michigan Museum
collection. The remains of young mastodons probably are overlooked
because of their small size. The recovery of these would contribute
greatly to our knowledge of milk teeth and tooth replacement.

A young adult, UMMP 29276, had the fourth upper right premolar in
use at the time of death. This tooth is well worn, and the first upper
molar shows wear on the anterior pair of cusps. The second molar ([M.sup.2]) had not moved down to the level of the grinding surface of
the first upper molar. The crown of the third upper molar ([M.sup.3]) is
fully developed, though it had not erupted.

In specimen UMMP 11308, the upper dentition of a young male, the
fourth upper premolar had been shed and the first molar had moved
forward in the jaw and taken its place. This tooth is well worn. The
second molar is worn on its anterior cusps and the third had not moved
into occlusal position (contact with opposite tooth). Specimen UMMP
24240 has the second upper molar well worn. The third molar is in
occlusal position and shows wear. Mastodons apparently had reached
maturity by the time the second and third molars were in use. The
University of Michigan Museum of Paleontology has no specimen in which
only the third molar was present, although this condition did occur in
aged animals (Hay 1914).

Tooth replacement in mastodons continued throughout much of their
life. In the majority of mammals milk teeth are pushed out by the upward
or downward growth of the permanent teeth that lie at their roots. In
the Proboscideans and Sirenians (Manatees and Dugongs) the permanent
teeth are formed in the back part of the jaw behind the milk teeth. As
the milk teeth are worn down, their replacements have to move forward
and upward in the lower jaws and forward and downward in the upper jaws.

Mastodons were neither as large nor as tall as mammoths in overall
body size, but the mastodon skull was larger and lacked the high
occipital crest so prominent in mammoth skulls (Plate I, Figure 1). The
mounted female mastodon in the University of Michigan Museum of
Paleontology measures approximately 7 feet, 8 inches tall at the
shoulders (Plate I, Figure 2). Adult males are taller.

Habitat and food. -- Mammut americanum was a forest animal,
browsing on the forest vegetation along bogs and streams (Hibbard 1951).
In the early days before scientific investigation, however, people who
found mastodon teeth thought them to have belonged to some large
flesh-eating monster (Jepsen 1960). Benjamin Franklin, who was one of
the first to study such teeth systematically, concluded that it would
have been impossible for the American mastodon to have eaten meat.

The following quotations are taken from Warren (1852), who mentions
three accounts of mastodon finds associated with materials which were
probably stomach contents.

Near Newburgh, in the State of New York, an American mastodon was
discovered in 1845. During the excavation of this animal, a mass of
material resembling crushed branches of trees was discovered.

According to Warren, a medical doctor, this material received
little attention at the time. Another man, Dr. Prime, was present at the
time of excavation and described the mass as follows:

In the midst of the ribs, imbedded in the marl and unmixed with shells
or carbonate of lime, was a mass of matter, composed principally of
twigs of trees broken into pieces of about two inches in length, and
varying in size from very small twigs to half an inch in diameter.
There was mixed with these a large quantity of finer vegetable
substance, like finely divided leaves; the whole amounting to from
four to six bushels. From the appearance of this, and its situation
(position in the skeleton), it was supposed to be the contents of the
stomach; and this opinion was confirmed on removing the pelvis,
underneath which, in the direction of the last of the intestines, was
a train of the same material, about three feet in length and four
inches in diameter. Microscopic examination of this matter revealed
that the twigs were terminal branches of coniferous trees.

Another mastodon from Chester, near Goshen, Orange County, New
York, had been discovered with similar vegetable material. Professor
Mitchell described it thus:

Beneath the bones, and immediately around them, was a stratum of
coarse vegetable stems and films resembling chopped straw, or rather
drift stuff of the sea; for it seemed to be mixed with broken fibers
of conferva, like those of the Atlantic shore.

[FIGURE 2 OMITTED]

The third occurrence reported was that of a mastodon from Wythe
County, Virginia, that was found associated with "half-masticated
reeds, twigs, and grass or leaves," according to Bishop Madison in
a letter to Dr. V. S. Barton.

The preservation of masticated vegetable matter from the stomach
should not be regarded as improbable because the finds are associated
with peat. Peat is an accumulation of vegetable material that has been
subjected to compaction for a very long period of time in bogs. It is
often well preserved, even to the extent that pollen grains occurring
within it can be examined and the genera of plants determined. Peat
deposits consist mostly of fine organic materials. Branches of trees are
not uncommon in such deposits, but these would never be "broken
into pieces of about two inches in length."

Location of finds of mastodon remains in Michigan. -- MacAlpin
(1940) listed 114 specimens of the American mastodon that had been found
in Michigan. He concluded that these represented considerably fewer than
half of those collected in the state since 1839. Forty-nine new
discoveries have since been reported. All of the recorded occurrences
within the state are shown in Figure 2. Following is a list of the new
records since 1939, obtained from newspaper articles, letters, and
museum specimens.

ALLEGAN COUNTY

1. Plainwell, 4 1/2 miles northeast. Gunplains Township, Sec. 10,
T.1 N., R.11 W. Most of a skeleton, lower jaw with teeth, many
vertebrae, no skull, fragments of ribs, sacrum, foot bones, etc., found
at a depth of 5 1/2 feet in marl.

2. Exact locality unknown. Parts of a skeleton. Specimen at the
Michigan State University Museum.

3. Exact locality unknown, but north of Grand Rapids. Humerus and a
few carpals. Specimen at the Grand Rapids Public Museum.

LAPEER COUNTY

1. Near Lapeer, about 5 miles southeast, Sec. 14, T.7 N., R.10 E.
Lower jaw with six cheek teeth and two small tusks, part of pelvis,
sacrum, two scapulae, 17 vertebrae, about 20 ribs, foot bones, parts of
radius, ulna, humerus, and femurs (UMMP 37811). A [C.sup.14] date was
obtained from this specimen. The date is 5950 [+ or -] 300 years before
the present (B.P.).

The mammoth arrived in North America from Eurasia much later than
the mastodon. The earliest records to date are from the early Middle
Pleistocene (Kansan deposits). This ancestral stock probably gave rise
to the Imperial mammoth and the Columbian mammoth (both southern forms)
and the Jefferson mammoth (a more northern species). The well-known
Woolly mammoth, a tundra dweller, arrived in North America much later in
the Pleistocene.

A census of the remains of Mammuthus jeffersoni has not previously
been reported for Michigan. Individual remains of this mammoth have in
the past been identified as the "Woolly" mammoth (M.
primigenius) or the Columbian mammoth (M. columbi). Hibbard (1951) only
briefly mentioned M. jeffersoni as occurring in the state.

Characters of Mammuthus jeffersoni. -- The teeth of mammoths, as
well as those of the living elephants to which the mammoths are related,
consist of alternating cement, dentine, and enamel ridge plates (Figure
1A; Plate III, Figures 1 and 2). These plates are transverse to the long
axis of the tooth. The number of ridge plates present in the tooth per
100 mm, the thickness of the enamel, and the distance of the enamel
plates from one another are used to distinguish the different species.
The premolars are smaller than the molars and hence possess fewer ridge
plates. The third molar is the largest tooth and has the most plates;
for the Jefferson mammoth, there are generally 25 in the upper and 24 in
the lower (M3 25/24). The symbols denoting the position of the teeth are
the same as those used to describe mastodon teeth. For mammoths and
elephants, however, after the symbol designating the tooth appears a
notation of the maximum number of ridge plates known for the upper and
lower teeth. The number of ridge plates observed in the upper tooth is
written above the line and the number in the lower tooth below the line.

Very few specimens of the Jefferson mammoth are in museum
collections in Michigan. The few remains that have been collected in the
state consist mostly of jaws with teeth or of isolated teeth. There are
remains of 3 individuals in the Grand Rapids Public Museum, 7 in the
Michigan State University Museum, and 9 in the University of Michigan
Museum of Paleontology. The most complete specimen yet found in the
state is represented by a partial skeleton (No. 8238) at the Michigan
State University Museum. This mammoth was found approximately 10 miles
southeast of Eaton Rapids on the Losey farm and consists of both lower
jaws, one tusk, many vertebrae, most of the ribs, the shoulder blades,
and a few leg bones. No skull or pelvis was found.

A lower jaw with two teeth, UMMP 22798, was found one mile north of
Assyria, in Barry County. This jaw was donated to the University of
Michigan Museum of Paleontology by Robert Hughes in 1942. It is from an
old individual; the anterior ridge plates of the last molars ([M.sub.3])
are worn down to their roots. The greatest anteroposterior length of the
left third molar (L[M.sub.3]) is 265.0 mm and the R[M.sub.3] is 255.0
mm. Both of these teeth have 18 ridge plates forming the occlusal
surface. L[M.sub.3] has 7 1/2 ridge plates in 100 mm and R[M.sub.3] has
7. The maximum width of R[M.sub.3] is 109 mm, as taken across the eighth
ridge plate, and the maximum width of L[M.sub.3] is 118.5 mm, as taken
across the 10th ridge plate. The distance between the grinding surface
of the two teeth anteriorly is 35.8 mm. The maximum width of the groove
above the rostrum is 70 mm, and the rostrum projects 80.4 mm beyond the
symphysis. The rostral groove between the jaws is constricted dorsally.
The greatest width of the jaws is 648.0 mm and the length is 542.0 mm.
The depth of the jaw, taken from the occlusal surface at the 13th ridge
plate to the base, is 223.0 mm. The mandibular condyles are 437.0 mm
above the base of the jaw.

Four associated teeth, UMMP 11735, a gift of George Wagner, were
found near the Chapel Hill School in Cass County. These are the upper
and lower third molars. L[M.sup.3] has 26 ridge plates, of which 18 make
up the grinding surface. In 100 mm there are 9 plates. R[M.sup.3]
consists of 26+ plates, with 18 making up the occlusal surface and 10
occurring within 100 mm. L[M.sub.3] consists of 25 plates plus one which
has broken off. The occlusal surface consists of 16 plates and there are
7 1/2 plates in 100 mm. R[M.sub.3] has 26 ridge plates, 17 of which form
the grinding surface. No accurate count could be made of the ridge
plates occurring in 100 mm because the tooth is slightly pathological.

As the above data show, there is considerable variation in
ridge-plate number, even in the same individual. The thickness of the
enamel forming the ridge plates, the number of these plates per tooth,
and the number occurring in 100 mm are the chief means by which the
various species of Mammuthus are distinguished. The specific
distinctions between the Woolly mammoth, the Columbian mammoth, and the
Jefferson mammoth, as set forth by Osborn (1936) may be summarized as
follows:

The Woolly mammoth Mammuthus primigenius is the animal that today
is found frozen in the Arctic regions of North America and Asia. It
roamed the tundra in great numbers late in the Pleistocene. It was
somewhat smaller than the Jefferson mammoth. The upper and lower third
molars have from 24-27 ridge plates, and from 9-13 plates per 100 mm,
with an average of 10 in most individuals. In comparison with the third
molars of the Jefferson mammoth, those of the Woolly mammoth generally
had more plates and were more compressed (which produced the higher
plate count per 100 mm).

Mammuthus columbi, the Columbian mammoth, was restricted to
southern North America, where it apparently was very abundant,
particularly in Florida. This species was larger than the Jefferson
mammoth. The enamel ridge-plate numbers for the third molars are
[18-19+]/[15-16+], and there are usually only 6 1/2 plates per 100 mm
(Osborn 1936, 1071). The enamel forming the ridge plates is thicker than
in either the Woolly or Jefferson mammoth.

Habitat and food. -- The mammoths were herbivores, as are the
living elephants to which all the mammoths are closely related. They
grazed on grasses of various kinds. Probably these animals confined
themselves to open grasslands and seldom entered deeply forested areas.
The Jefferson mammoth was apparently rather rare in Michigan. This
scarcity may be accounted for by limited meadow areas, which would
reduce the number able to live in the state. The rarity of finds may be
due, in part, to the mammoths' preference for an upland habitat,
where their remains would seldom be preserved.

Stomach contents are known only from frozen bodies of the Woolly
mammoths (Farrand 1961). Felix (1912) reported a frozen Woolly mammoth
from Siberia that had within its stomach various tundra grasses, such as
red bent grass and alpine foxtail. The needles of conifers were rare in
the material examined. Heintz (1955) mentioned the types of vegetation
found in the stomach of a frozen Woolly mammoth as being mosses and
grasses. A pollen analysis of the stomach contents of the
Beresovka-mammoth (Heintz 1955) showed that 97.09 percent of the pollen
belonged to grasses and only 0.17 percent belonged to trees (fir, alder,
birch, willow). The rest of the pollen belonged to various other meadow
plants.

There is no reason to believe that the Jefferson mammoth deviated
from a herbivorous, grazing mode of life. The species of plants for this
mammoth would be different from those forming the diet of the Woolly
mammoth, but most were probably grasses. Possibly in the winter months
some alder, willow, and birch supplemented this fare. In character the
teeth in the Jefferson mammoth are most like those of the Asiatic
elephant, which is almost exclusively a grazer.

Location of finds of the Jefferson mammoth in Michigan. --
Thirty-two Jefferson mammoth remains have been recorded in Michigan
since 1839. As in the case of the mastodon, this number probably
represents considerably fewer than the remains actually found in the
state. Recorded occurrences are shown in Figure 3 and listed below.

[FIGURE 3 OMITTED]

ARENAC COUNTY

1. 2 1/2 miles north of Au Gres. One tooth (letter of W. A. Kelly,
September 24, 1935). Specimen at Michigan State University.

1. Near Eaton Rapids, 9 1/2 miles southeast. Both lower jaws; one
tusk; cervical, thoracic, and lumbar vertebrae; most of the ribs; both
shoulder blades; and two or three leg bones, in marl. Specimen at the
Michigan State University Museum, No. 8238.

2. Locality not known, somewhere in the northern part of Jackson
County. One molar (UMMP 3163), in peat.

KENT COUNTY

1. Grand Rapids, approximately 5 miles south on Plaster Creek. One
tooth.

Very few mastodons and mammoths have been collected in the state in
recent years, chiefly because of the use of heavy machinery instead of
hand labor to dig out muck. When drainage ditches and the like were dug
by hand or with oxen or horses, the chances were greater for a bone to
be noticed and recovered. Few mastodons and mammoths have become
available for radiocarbon ([C.sup.14]) dating since the establishment of
the University of Michigan radiocarbon dating laboratory in 1950. The
specimens collected before this date were treated with alvar or shellac
and are thus worthless for the radiocarbon method (Hibbard and Hinds
1960). It has been found that ivory, because of its compactness, is far
better for use in [C.sup.14] dating than bone. Bone often becomes
contaminated by the intrusion of small roots and rootlets of recent
plants and hence will give an erroneous date.

Part of a mastodon tusk (M-67, Crane 1956) was submitted to the
University of Michigan Memorial-Phoenix Project Laboratory for
radiocarbon dating. It was partially mineralized. Its source was a
gravel pit consisting of Cary outwash in the NE 1/4 Sec. 4, T.3 S., R.4
E., Freedom Township, Washtenaw County, Michigan. The sample from the
tusk dated 6100 [+ or -] 400 B.P. from carbon black and 6300 [+ or -]
500 B.P. from a gas sample. It should be noted that acid soluble
carbonates from the tusk were used to obtain the samples. The gravels in
the exposure are chiefly limestone, and considerable calcium carbonate cementing had occurred in the area in which the tusk was found. The
radiocarbon date, therefore, is in error. Dating of the Cary stage (the
age of the glacial outwash gravels), is between 13,000 and 15,000 B.P.
(Flint 1957; Frye and Willman 1960), which may give a more reliable
estimate of the age of the tusk.

The following [C.sup.14] dates for American mastodons were obtained
from samples of tusks with one exception, when part of a rib was used.
The samples used in dating are given numbers preceded by the letter M,
which stands for the University of Michigan radiocarbon dating
laboratory. Unfortunately, no dates are available for Jefferson mammoth
bones or tusks.

Hester (1960) states that most of the large Pleistocene herbivores
in North America became extinct around 8,000 years ago, as indicated by
radiocarbon dates. According to his data, the mammoths apparently died
out earlier than the American mastodon. The latter probably survived a
little later in isolated areas. According to the above radiocarbon
dates, the American mastodon became extinct somewhere after 6,000 years
ago. This is approximately the time of the beginning of recorded
history.

In most cases the causes of extinction are unknown. It is usually
impossible to know exactly why a species of animals could not maintain
its numbers. Seldom can a single factor be considered the sole cause.
The extinction of the American mastodon and the Jefferson mammoth
probably was the result of a number of unfavorable conditions that acted
at the same time.

It is known that the Late Pleistocene American Indians of the
southwest hunted the now-extinct Columbian mammoth (Wormington 1957), a
close relative of the Jefferson mammoth. There is as yet no evidence
that early man hunted either the mammoth or mastodon in Michigan.

It is possible that extinction of the American mastodon was partly
brought about by the barrier formed by the Great Lakes. Because of this
barrier the mastodons might have been unable to follow the northward
retreat of the boreal forest environment as the forests followed the
retreat of the last glacier. Other barriers were formed by the
grasslands and Glacial Lake Agassiz to the northwest. The north outlet
to the northeast would offer similar restrictions, since it served as a
vast floodway for glacial meltwater.

Recently much work has been done on fossil pollen contained in peat
from bogs. The genera of plants represented by the fossil pollen can
usually be determined, and radiocarbon dates can be obtained from wood
associated with it. From the fossil pollen and its chronology, the type
of forest that was present around the bog can be determined for a given
time. Two studies from southern Michigan, one from near South Haven, and
the other from a bog near Hartford, revealed the following forest
changes for these areas (Zumberge and Potzger 1956). A forest consisting
chiefly of spruce and some fir was present in southern Michigan 11,000
years ago. This would point to a cool to cold, moist climate. The end of
the spruce-fir forest occurred around 8,000 years ago, followed by an
increase of pine. The maximum development of pine in southern Michigan
was around 6,000 years ago, indicating a warming and drying climate.
Associated with the pine was oak and hickory. Approximately 5,000 years
ago pine had declined in importance and there was an increase of oak,
chestnut, and hickory. The climate at this time was warmer and dryer
than at any earlier time in the Late Pleistocene. Since 5,000 years ago,
the forest in southern Michigan has consisted mostly of oak, chestnut,
hickory, and other broad-leaved species.

Mastodons in Michigan were adapted to life in a mixed coniferous and broad-leaved forest. A mature evergreen forest, composed of large
trees with their lowest branches well off the ground, would provide poor
browse for these animals and thus cause a decline in their numbers. A
mature coniferous forest would have been barren of young seedlings
because of the deep shade the large trees produced. Radiocarbon dating
indicates that broad-leaved trees became abundant around 5,000 years
ago.

I wish to thank the following persons for granting permission to
examine the specimens under their care and for access to the records
pertaining to these specimens: Edward Brigham, Kingman Museum, Battle
Creek; Frank L. Du Mond, Grand Rapids Public Museum; Rollin H. Baker,
Michigan State University Museum; Lester E. Eyer, Alma College; and
Lewis B. Kellum, University of Michigan Museum of Paleontology. I
especially wish to express my gratitude to Claude W. Hibbard for his
advice and criticism during the preparation of this paper, and to John
A. Dorr, William S. Benninghoff, and Katharine A. Fellows for reading
the manuscript and giving helpful suggestions.

I am also grateful to Edwin H. Colbert, of the American Museum of
Natural History, for providing the picture of the Jefferson mammoth
skeleton for publication. I also wish to thank Herbert W. Wienert for
taking most of the other photographs.

Originally published in Papers of the Michigan Academy of Science,
Arts, and Letters Pt. 1 (1962): 101-33.

_____. 1923. The Pleistocene of North America and its Vertebrated
Animals from the States East of the Mississippi River and from the
Canadian Provinces East of Longitude 95[degrees]. Carnegie Inst. Wash.
Publ., No. 322: 1-499, 41 pls., 25 figures.